Additive to sand moulds and cores



United States Patent ADDITIVES T0 SAND MOULDS AND CORES Derek PriestleyHelliwell, Birmingham, England, assignor to Foseco InternationalLimited, Birmingham, England,

a British company No Drawing. Filed July 21, 1965, Ser. No. 473,851Claims priority, application Great Britain, Aug. 20, 1964,

34,116/64; Nov. 24, 1964, 47,774/64; Dec. 31, 1964,

8 Claims. (Cl. 106-385) ABSTRACT OF THE DISCLOSURE Pinning or veiningproduced on metal casting cast in sand moulds or around sand cores maybe minimised by the incorporation into the sand mould or core of aproportion of colemanite or unexpanded perlite.

This invention relates to said moulds and cores and more particularly toadditives for sand moulds and cores which improve the characteristicsthereof. The invention may be applied to sand moulds and coresincorporarting any organic binder but it is of greatest practical valuein connection with oil-bonded sand cores as hereinafter set forth.

The invention is concerned with the production of castings fromnon-skin-forming metals which are poured at above 750 C. Such metals arethe cast irons (grey or modular) and copper based alloys such as lead-,tinand Phosphor-bronzes.

In producing castings of such metals using moulds or cores of oilbondedor resin-bonded natural, synthetic or semi-synthetic silica sands (i.e.which contain less than clay), which have a high dry compressionstrength, a ditiiculty sometimes arises which is known in the art asfinning or veining. When such a sand core is heated by the molten metalit may develop surface cracks. The molten metal tends to enter thesecracks and in consequence when the casting is stripped away from thecore it may have projections corresponding to these cracks, so calledfins or veins which of course must, where possible, afterwards beremoved from the casting by a machining operation. The phenomenon offinning and veining thus leads to an increase in overall productioncosts. Moreover in some cases, e.g. where the finning or veining occursin a narrow passage way of the casting, the removal of the fins or veinsmay not be a practical possibility.

The incidence of finning or veining appears to vary with the nature ofthe bonding agent. Sand moulds and cores which have inorganic binders,e.g. which are bonded with silicate, appear to show little tendencytowards this phenomenon and such moulds and cores are therefore notincluded within the scope of this invention.

Sand moulds and cores in which the bonding agent is oil, Le. a drying orsemi-drying oil such as linseed, tung or oilicica, or mixtures of any ofthese, the oil being optionally in association with a cerealcarbohydrate or the like, which usually include a metal, e.g. cobalt orlead, naphthenate as hardener, and which require stoving before use,show some tendency to finning and veining. Sand moulds and cores inwhich the binder is an air-drying oil (as above) together with anaccelerator, e.g. an inorganic peroxy compound such as sodium perborate,show a slightly greater tendency to finning and veining. Theresin-bonded sand moulds and cores generally exhibit the phenomenon toan appreciably greater extent: e.g. in the case of furane bonding resinswhich are set by heating the problem is very severe and in the case offurane bonding resins which are cold set the problem, though stillsevere, is not quite so serious.

It is an object of the present invention to provide oilbonded orresin-bonded synthetic or washed silica sand moulds and cores of highdry compression strength, especially cores which contain certainadditives tending to reduce the incidence of finning or veining to beused for casting non-skin forming metals.

According to the present invention, there is provided an oil-bonded orresin-bonded natural, synethetic or semisynthetic silica sand mould, orcore containing less than 5% of clay, for use in casting non-skinforming metals, having a dry compression strength of more than 14 kg./sq. cm. which includes as an additive to the composition of the sandmould or core, potassium nitrate, colemanite, unexpanded perlite, bariumsulphate, sodium rnetaphosphate or potassium alum, or a mixture of anyof said substances.

The reason why these substances function is not understood, especiallysince they are inherently dissimilar in chemical and physicalproperties. Potassium nitrate, barium sulphate, sodium metaphosphate andpotassium alum are relatively simple chemical substances thecharacteristics of which are well known. Colemanite is a commerciallyavailable mineral of the approximate formula 2CaO-3B O -5H O. Anaturally occurring hydrated calcium tetraborate, which in the anhydrousform melts at nearly 1000 C. and is also known as bore-calcite, andperlite is a mineral which, on heating, exfoliates to reduce its initialdensity of between 2 and 3 to a value very much below 1. It is believedthat each of these substances acts in its own way to facilitate relativemovement of the sand grains so that the expansion of the mould or coreon heating can be taken up by the material of the mould or core withoutgiving rise to cracking.

Generally speaking the quantity of said substance or mixture of saidsubstances suitable for addition to the material of the mould or coremay be within the range 0.5 to 5% of the total weight of the dry mouldor core, although a somewhat higher proportion may be requiredoccasionally.

It is to be noted however that a successful additive should not onlyprevent finning, but also maintain strength, the knock out propertiesshould not be affected, nor must the bonding properties of the oil orthe polymerisation of the resin be inhibited. The gas evolution must notbe increased and the surface finish should be improved rather thanimpaired. The additives of this invention tend to fulfill all theserequirements.

Where the binder for the sand is a resin it is preferably a furane resinbut other resin binders may be employed, e.g. phenol-formaldehyde orurea-formaldehyde resins. If desired there may be used, with any suchresin binder, a diluent liquid which will assist in providing a suitablymouldable sand mix. The diluent liquid, if used, should of course nothave any deleterious inhibitory effect on the polymerisation orpolycondensation of the resin whereby the resin hardens to give a rigidproduct. Suitable liquids for the purpose are inert mineral oils and theoil product sold commercially under the trademark Dutrex 55.

The use of the special additives of the present invention makes itpossible to use a smaller amount of the resin binder While stillobtaining a desired strength in the final product. The inclusion of aliquid diluent as just described makes the use of such smallerquantities of resin binder easier to handle in practice.

However, while the additives of the present invention reduce theincidence of finning or veining in such resinbonded sand moulds andcores the additives are not aL ways wholly successful in totallyeliminating the phenomenon. On the other hand, applied to oil-bondedsand resins and cores as referred to above, substantially completeelimination of the finning and veining is achieved. The followingexamples will serve to illustrate the invention EXAMPLE 1 To Kings Lynn85. sand, at fine washed silica sand, bonded with a hot-box furaneresin, was added 0.5% by weight of the dry sand of the additives listedbelow. This mixture was milled until evenly dispersed. 0.15% of acatalyst for a furane-type hot-box resin was then added and the mixturemilled again followed by 2% by weight of a furane-type hot-box resin andthe mixture milled again until all the additives were evenly distributedthroughout the sand. The mixture was then fed to a conventional foundrycore blower for the manufacture of cores, by the hot-box technique.These cores were incorporated in foundry moulds for the manufacture ofcastings of low phosphorus cast iron which was poured at 1400 C.

The following results show that the three additives of this inventioneither used singly or in combination all tend to reduce finning onnon-skin forming metals.

Percent composition of additive Dry strength, Finning The following sandmix was used for the manufacture of cores, for the manufacture of castiron castings:

Congleton sand kg 181.6 Dextrin kg 2.72 Core oil c" 1120 Water cc 1680Anti-finning (50/50 mixture of colemanite and unexpanded perlite) kg1.82

Cores manufactures from this mixture had a dry compression strength of57 kg./sq. cm. (this compares with the strength of approximately only 42kg./sq. cm. when used without the anti-finning additive) and thecastings produced were entirely free from veins or fins whereas therehad previously been a severe level of scrapped castings because of theincidence of such faults.

I claim as my invention:

1. Oil-bonded and resin-bonded natural, synthetic and semi-syntheticsilica sand moulds and cores containing less than 5% of clay, for use incasting non-skin forming metals, having a dry compression strength ofmore than 14 kg./sq. cm. which include as an additive to the compositionthereof, at least 0.5% by weight of a substance selected from the classconsisting of colemanite and unexpanded perlite.

2. A mould or core for use in casting non-skin forming metals whichcomprises essentially silica sand containing less than 5% by weight ofclay and bonded by means of a drying oil and a cereal carbohydrate, andhaving a dry compression strength of more than 14 kg./sq. cm. whichincludes as an additive to the composition thereof, at least 0.5% byweight of a substance selected from the class consisting of colemaniteand unexpanded perlite.

3. A mould or core for use in casting non-skin forming metals whichcomprises essentially silica sand containing less than 5% by weight ofclay and bonded by means of a drying compression strength of more than.

14 kg./sq. cm. which includes, as an additive to the compositionthereof, at least 0.5% by weight of colemanite.

4. A mould or core for use in casting non-skin forming metals whichcomprises essentially silica sand containing less than 5% by weight ofclay and bonded by means of a drying oil and a cereal carbohydrate, andhaving a dry compression strength of more than 14 kg./sq. cm. whichincludes, as an additive to the composition thereof, at least 0.5% byweight ofunexpanded perlite.

5. Oil-bonded and resin-bonded natural, synthetic and semi-syntheticsilica sand moulds and cores containing less than 5% of clay, for use incasting non-skin forming metals, having a dry compression strength ofmore than 14 kg./sq. cm. which include as an additive to the compositionthereof, a substance selected from the class consisting of colemaniteand unexpanded perlite, the said additive being present in a proportionof 0.5 to 5% by weight of the composition.

6. A mould or core for use in casting non-skin forming metals whichcomprises essentially silica sand containing less than 5% by weight ofclay and bonded by means of a drying oil and a cereal carbohydrate, andhaving a dry compression strength of more than 14 kg./ sq. cm. whichincludes as an additive to the composition thereof, a substance selectedfrom the class consisting of colemanite and unexpanded perlite, the saidadditive being present in a proportion of 0.5 to 5% by weight of thecomposition.

7. A mould or core for use in casting non-skin forming metals whichcomprises essentially silica sand containing less than 5% by weight ofclay and bonded by means of a drying oil and a cereal carbohydrate, and

having a dry compression strength of more than 14 r kg./sq. cm. whichincludes, as an additive to the composition thereof, colemanite, thesaid additive being present in a proportion of 0.5 to 5% by weight ofthe composition.

8. A mould or core for use in casting non-skin forming metals whichcomprises essentially silica sand containing less than 5% by weight ofclay and bonded by means of a drying oil and a cereal carbohydrate, andhaving a dry compression strength of more than 14 kg./sq. cm. whichincludes, as an additive to the composition thereof, unexpanded perlite,the said additive being present in a proportion of 0.5 to 5% by weightof the composition.

References Cited UNITED STATES PATENTS 2,237,592 4/1941 Dunbeck l06-38.92,426,000 8/1947 Cutler 106--38.7 X 2,789,331 4/1957 Dietert 22---l932,797,457 7/1957 Kramer 22-493 2,974,050 3/1961 Barlow 10638.5 3,104,2309/1963 Dewey et al 22193 X ALEXANDER H. BRODMERKEL, Primary Examiner.

DONALD J. ARNOLD, Examiner.

L. B. HAYES, Assistant Examiner.

